High pressure mercury discharge lamp

ABSTRACT

A high pressure discharge lamp containing metal halides in the fill and having a power input of more than 1,000 W is dimensioned such that the ratio of electrode spacing to inner diameter of the envelope is between 0.05 and 1 per kW of power input, and the ratio of power input in watts to volume in cubic centimeters is between 10 and 100. The lamp is operated with a current intensity of at least 25 amperes and preferably has a high-current seal, the main constituent thereof being a cup of molybdenum with its bottom closing off the discharge space. Intense molecular radiation is emitted from a broad annular zone surrounding the discharge core and occupies at least 80% of the lamp diameter.

1 July 29, 1975 HIGH PRESSURE MERCURY DISCHARGE LAMP [75] Inventors: Hanns-Peter Popp; Horst Grabner,

both of Munich, Germany [73] Assignee: Patent-Treuhand-Gesellschaft fur Elecktrische Gluhlampen mbH, Munich, Germany 22 Filed: Mar. 19, 1974 21 App]. No.: 452,639

[30] Foreign Application Priority Data Apr. 6, 1973 Germany 2317461 [52] U.S. Cl 313/214; 313/228 [51] Int. Cl. H01J 17/04 [58] Field of Search 313/214, 217, 219, 225,

[56] References Cited UNITED STATES PATENTS 2.650.322 8/1953 Francis ct a1. 313/214 2,714,686 8/1955 Isaacs et a1. 313/214 FOREIGN PATENTS OR APPLICATIONS 508,525 12/1954 Canada 313/225 Primary ExaminerJames B. Mullins Attorney, Agent, or FirmFlynn & Frishauf [57] ABSTRACT A high pressure discharge lamp containing metal halides in the fill and having a power input of more than 1,000 W is dimensioned such that the ratio of electrode spacing to inner diameter of the envelope is between 0.05 and 1 per kW of power input, and the ratio of power input in watts to volume in cubic centimeters is between 10 and 100. The lamp is operated with a current intensity of at least 25 amperes and preferably has a high-current seal, the main constituent thereof being a cup of molybdenum with its bottom closing off the discharge space. Intense molecular radiation is emitted from a broad annular zone surrounding the discharge core and occupies at least 80% of the lamp diameter.

10 Claims, 2 Drawing Figures HIGH PRESSURE MERCURY DISCHARGE LAMP This invention relates to improved high pressure discharge lamps having a power input greater than 1,000 W.

Lamps of this general type, i.e., high pressure discharge lamps, are used for general lighting purposes. Such lamps have an arc length which is a multiple of the lamp diameter. The arc burns in a constructed space filling less than one-half the cross section of the bulb, that is the lamp envelope or discharge vessel surrounding the electrodes and occupied by the arc and the fill material. These lamps have a mercury fill and also contain metal halides including the halides of the rare earth metals (see German Pat. No. 1184008 and German disclosure document No. 2106447). A special type of high pressure mercury discharge lamps are used for special lighting applications. Such lamps have are lengths which are shorter than those of the types of lamps used for general lighting purposes. They have an arc of medium length which also occupies a constricted space. Specific load per centimeter of arc length as well as the wall loads in such lamps is higher than in the lamps used for general purposes. The fill of such lamps also contains mercury and the rare earth metal halides (see US. Pat. No. 3,654,506 and German disclosure document No. 2114804). Such lamps have excellent color rendering characteristics and are thus well suited for such uses as color television pickup and color photography.

The known high pressure discharge lamps which contain the said metal halides are atomic radiators and emit a line spectrum in the visible region. In addition to the linear radiant emission in these known lamps there is also observed a weak continuum, especially in case of high loads, which originates from the small aureole in the outer regions of the arc. The color of the aureole is dependent on the respective metal which is excited in the discharge. The present invention provides improved lamps with an increased total emission including a substantially increased rate of the continuum emission.

SUBJECT MATTER OF THE INVENTION:

The present invention provides high pressure discharge lamps comprising a bulb of transparent material of high heat capacitance and having a power input in excess of 1,000 W (watts). The bulb includes spaced apart electrodes. The improved lamps are characterized by having (a) a ratio of electrode spacing to the inner diameter of the bulb (arc tube diameter) of between 0.05 and 1 per kW of power input for the lamp and (b) having a ratio of power input in watts to the volume of the discharge are in cubic centimeters of between and 100. The said volume of the discharge arc is that portion of the bulb (also referred to as the envelope or arc tube) which extends between the electrodes. Preferably, the ratio of electrode spacing to inner diameter is from about 0.1 to 0.5 kW of power input of the lamp and the preferred ratio of power input in watts relative to the volume of the discharge arc in cubic centimeters is about -50.

The lamp fill comprises a noble gas as the basic gas, mercury, and the rare earth metal halides, preferably dysprosium.

The lamps of the present invention are operated with high intensity current, preferably at least amperes,

especially when using high power input. Because the lamps utitize this high intensity current, the lamps are constructed with a seal comprising a cup of refractory metal suitably molybdenum, at each end. The said cup is positioned with its bottom closing off the arc discharge space. The sleeve of the cup tapers toward the end of the cup away from its bottom and is hermetically sealed to the lamp stem. The lamp stem preferably consists of quartz and Vycor. Each of the electrodes is attached to a lead-in rod which is inserted through the bottom of the cup and hermetically sealed therein. Heat accumulating annular grooves are placed in the lead-in rod and positioned immediately in front of the cup bottom in the direction of the electrode. A supporting disc is affixed to the lead-in rod and positioned behind the cup bottom in the direction away from the electrode. The lamp stem material preferably not only is in contact with the outer surface of the cup but extends around the end and abuts the face of the supporting disc. This abutting material of the lamp stem thereby completely seals the discharge space. The lamp bulb surrounding the arc discharge may be enclosed in an outer envelope or jacket which is preferably filled -with a low pressure gas having strong dielectric characteristics. The invention will be described by way of example with reference to the accompanying drawings wherein:

FIG. 1 is a cross section of a lamp according to the invention; and

FIG. 2 illustrates the spectral distribution of the radiant flux emitted by the lamp.

With reference to FIG. 1, the discharge vessel 1 is of quartz glass with a wall 13 thickness of 2-3 mm. Its inner diameter is 60 mm. Disposed in each end of the vessel 1 is an electrode 2 and 3 of refractory metal such as tungsten. The electrode spacing, i.e., the distance between the opposed electrode, is 50 mm. The lead-in rods 4 and 5 of the electrodes are of tungsten and are hermetically passed through the bottom 6 of molybdenum cup 7. They are provided with heat accumulating grooves 8 and carry a supporting disk 9 with the lamp stem material of quartz and Vycor closely abutting the disk. The hermetic closure of the seal is effected at the cup border 10 by the stem material 15 which surrounds the cup side wall 14. The lamp bulb surrounding the arc discharge is enclosed in an outer envelope or jacket, shown schematically in vertical lines J, which is preferably filled with a low pressure gas having strong dielectic properties.

The discharge vessel 1 is filled with Xenon of 50 torr, 150 mg of mercury, 33 mg of PyJ and 10 mg of Ti]. The volume of l is cc. The temperature of the inner surface of wall 13 of the discharge vessel 1 is approximately 900C, and the operating pressure is about 2 atm. The foregoing fill quantities and structural data are for a lamp with a power input of 4 kW and operated from 220 V A.C. The operating voltage is V, the current intensity 40 amps. The lamp operates in all operating positions. The power input is about 36 W per cubic centimeter. The ratio of electrode spacing to inner diameter of the discharge vessel per kW is about 0.2. The luminous efficacy is 100 lm/W. The color rendering index exceeds 90.

FIG. 1 also schematically illustrates the setup (form) of the discharge. Around the narrow, high intensity discharge core 11 of high temperature which emits atomic radiation, there extends a broad annular zone 12 (aureole) of lower temperature from which molecular radiation originates. The are width is about 90% of the diameter of the discharge vessel.

The distribution of radiant flux standardized to a luminous flux of 1000 lumens is illustrated in FIG. 2.,The emission proceeds uniformly across. the entire visible spectral region. There is a remarkably high red component which is emitted by the broad annular zone of the discharge as molecular radiation of the dysprosium iodide.

With the lamps of the presentinvention it has been established that the arc is broader than in the prior art lamps and occupies at least 80% of the diameter of the discharge vessel and in most instances 90% or above. The prior art would have expected a disadvantageous decrease in luminous efficacy with such an increase in the breadth of the arc and instead it has been found that this does not occur.

The improved lamps of the present invention include a narrow, high intensity discharge core of high temperature from which atomic radiation is emitted. Unexpectedly, it has been found that a broad annular Zone of lower temperature which emits continuum radiation of an appreciable intensity is formed around the said high intensity discharge core. Because of the lower temperature, the metal halides in said annular zone are not dissociated. Therefore, the. continuum radiation from said zone represents a molecular radiation from the metal halides. This follows since the spectra are characteristically dependent upon the respective metal and the respective halogen. The characteristic radia-,

tion maxima of the metal are shifted to shorterwavelengths for each metal halidewhen substituting bromine for iodine.

The advantages of the improved lamps of the present invention are that high intensity is produced with a short arc length which is a favorable condition for optical efficiency. The low wall load is advantageous in connection with the service life of the lamp. The intense molecular radiation emitted from a large volume tric space of the arc provides a desirable radiation component, especially in the red spectral region. These lamps can be operated with high current intensities and therefore it is possible for the first time to operate lamps from 220 V A.C. even with power inputs in excess of 3 kW.

When comparing the prior art high intensity lamps discussed hereinbefore, advantages become evident for the improved lamps of the present invention. Thus, the medium-arc length prior art lamps had ratios of electrode spacing to the inner diameter with respect to power input which in part compare with those of the improved lamps. However, this prior art configuration results in a much higher ratio of power input to volume than in the lamps of the present invention and as a result absolute dimensions are considerably smaller and consequently, the inner wall temperatures become extremely high which is disadvantageous. The general purpose lamps of the prior art have ratios of power input to volume of the lamp which in part compare with those of the improved lamps of the present invention. However, the ratio of the electrode spacing to inner diameter of these lamps with respect to power input is higher than with the improved lamps of the present invention. Consequently, the inner diameter of the lamps of the present invention is larger. It has been discovered that in spite of this larger inner diameter, the arc discharge of the improved lamps is most unexpectedly wall-stabilized. Based on the knowledge of the aforesaid prior art high intensity lamps, it would have been expected that lamps with a larger diameter relative to the electrode spacing would have an unstable arc and.

an appreciable decrease in the luminous efficacy. This would have been expected to result from the expected lower wall temperature and consequent lowering in vapor pressure of the metal halide. Instead, it has. been discovered that the improved lamps of thepresent invention have improved luminous efficacy. Vycor is a trademark of the Coming Glass Works company and is for a borosilicate glass material.

We claim:

l. An improved high pressure mercury discharge lamp having a power input in excess of 1,000 watts comprising spaced apart electrodes in a bulb of transparent material having high heat capacity and containing metal halides, the improvement comprising the combination wherein the ratio of electrode spacing to inner diameter of the bulb is between 0.05 and l per kilowatt of power input to the lamp, and the ratio of power input in watts to volume of the discharge are in cubic centimeters is from 10 to 100.

2. The lamp of claim 1, wherein said ratio of electrode spacing to inner diameter is from. 0.1 to 0.5 per kilowatt of power input, and the said ratio of power input in watts to volume of the discharge are in cubic.

centimeters if from 20 to 50.

3. The lamp of claim 1, wherein the width of the luminous portion of the discharge arc is at least of the diameter of the said bulb.

4.The lamp of claim 1, wherein the width of the luminous portion of the discharge, are is at least of the diameter of the said bulb.

'5. The lamp of claim 1, wherein the said lamp is adapted to a current intensity input of atleast 25 am-.

peres.

6. The lamp of claim 3,. wherein the said lampis adapted toa current intensity input of at least 25 amperes.

7. The lamp of claim 1 having at each end a high current seal hermetically sealed to said bulb, said seal comprising a cup-shaped refractory metal with the cup bottom facing the interior of said bulb and having cup walls which taper in the direction away from the cup bottom and are hermetically sealed to said bulb, and having a lead-in rod of refractory material hermetically passed through the bottom of said cup, said lead-in rod having an electrode attached at its inner end thereof and being provided with annular grooves for heat accumulation directly in front of said cup bottom in the interior direction of said bulb and having a supporting disk positioned behind said cup bottom, and saidbulb material abutting the surface of said disk and said tapered cup walls.

8. The lamp of claim 6 having at each end a highcurrent seal hermetically sealed to said bulb, said seal comprising a cup-shaped molybdenum with the cup bottom facing the interior of said bulb and having cup walls which taper in the direction away from the cup bottom and are hermetically sealed to said bulb, and having a lead-in rod of refractory material hermetically passed through the bottom of said cup, said lead-in rod having an electrode attached at its inner end thereof and being provided with annular grooves for heat accumulation directly in front of said cup bottom in the in- 6 terior direction of said bulb and having a supporting in an outer envelope or jacket. disk positioned behind said cup bottom, and said bulb material abutting the surface of said disk and said tapered cup walls.

9. The lamp of claim 8, wherein said bulb is enclosed 5 10. The lamp of claim 1, wherein said bulb is enclosed in an outer envelope or jacket.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,89'7,594 Dat d July 29, 1975 Inventor(s) HANNS-PETER POPP et al It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Column -l, line 9 correct the spelling of "constricted" Column 2, lines 48-49, correct the spelling of "dielectric".

Column 2 line 51, replace "PyJ with --DyI same line replace "'IiJ" with TlI-.

Column 4 line 29 replace "if" with --is.

Signed and Scaled this sixth D y of January 1976 [SEAL] A ttes t:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ufPatents and Trademarks 

1. An improved high pressure mercury discharge lamp having a power input in excess of 1,000 watts comprising spaced apart electrodes in a bulb of transparent material having high heat capacity and containing metal halides, the improvement comprising the combination wherein the ratio of electrode spacing to inner diameter of the bulb is between 0.05 and 1 per kilowatt of power input to the lamp, and the ratio of power input in watts to volume of the discharge arc in cubic centimeters is from 10 to
 100. 2. The lamp of claim 1, wherein said ratio of electrode spacing to inner diameter is from 0.1 to 0.5 per kilowatt of power input, and the said ratio of power input in watts to volume of the discharge arc in cubic centimeters if from 20 to
 50. 3. The lamp of claim 1, wherein the width of the luminous portion of the discharge arc is at least 80% of the diameter of the said bulb.
 4. The lamp of claim 1, wherein the width of the luminous portion of the discharge arc is at least 90% of the diameter of the said bulb.
 5. The lamp of claim 1, wherein the said lamp is adapted to a current intensity input of at least 25 amperes.
 6. The lamp of claim 3, wherein the said lamp is adapted to a current intensity input of at least 25 amperes.
 7. The lamp of claim 1 having at each end a high-current seal hermetically sealed to said bulb, said seal comprising a cup-shaped refractory metal with the cup bottom facing the interior of said bulb and having cup walls which taper in the direction away from the cup bottom and are hermetically sealed to said bulb, and having a lead-in rod of refractory material hermetically passed through the bottom of said cup, said lead-in rod having an electrode attached at its inner end thereof and being provided with annular grooves for heat accumulation directly in front of said cup bottom in the interior direction of said bulb and having a supporting disk positioned behind said cup bottom, and said bulb material abutting the surface of said disk and said tapered cup walls.
 8. The lamp of claim 6 having at each end a high-current seal hermetically sealed to said bulb, said seal comprising a cup-shaped molybdenum with the cup bottom facing the interior of said bulb and having cup walls which taper in the direction away from the cup bottom and are hermetically sealed to said bulb, and having a lead-in rod of refractory material hermetically passed through the bottom of said cup, said lead-in rod having an electrode attached at its inner end thereof and being provided with annular grooves for heat accumulation directly in front of said cup bottom in the interior direction of said bulb and having a supporting disk positioned behind said cup bottom, and said bulb material abutting the surface of said disk and said tapered cup walls.
 9. The lamp of claim 8, wherein said bulb is enclosed in an outer envelope or jacket.
 10. The lamp of claim 1, wherein said bulb is enclosed in an outer envelope or jacket.
 100. 